# Ch3.2 and 3.3.

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Ch3.2 and 3.3

Fluids What do liquids and gases have in common? States of matter
Do not have a fixed shape Ability to flow, particles can move past each other easily

Buoyant Force Why doesn’t a rubber duck sink to the bottom of a bath tub? A force pushes the rubber duck to the top of the water.

Buoyant Force This force is an upward force that fluids exert on matter. What keeps the ice floating?

Ice cube floating in water
The pressure exerted on the right is equal to the pressure exerted on the left. Theses forces cancel out.

Ice cube floating in water
Pressure increases as depth increases. Pressure increases Net force is upward (buoyant force)

Archimedes’ principle
The buoyant force on an object is an upward force equal to the weight of the fluid that the object displaces.

Change the shape of an object and you can change the density.

A solid brick’s density is 1. 9g/cm3. And the density of water is 1
A solid brick’s density is 1.9g/cm3. And the density of water is 1.00g/cm3 . How could you get the brick to float?

Where have you heard the word “pressure” in conversation?
Air pressure Water pressure Tire pressure Blood pressure

Pressure When you pump up a bike tire, what is going on inside the tire?

Pressure

Pressure Pressure is calculated by using the equation below.
pressure = Force area Pressure unit is pascal (Pa). It is equal to 1N/m2

Pascal’s Principle When you blow a bubble, you blow air in one direction. So why does the bubble get rounder as you blow, instead on longer? Fluid property: Fluids exert pressure evenly in all directions.

Pascal’s Principle P1 = P2 So our equation can now look like this:
F1 = F2 A1 A2

Pascal’s Principle

What do you observe?

Fluids in motion Give an example of a moving fluid. air moving as wind
water moving through pipes food coloring moving through water

Fluids in motion Fluids move faster through smaller areas than through larger areas

Viscosity How are honey and lemonade similar? How are they different?
Viscosity is a liquid’s resistance to flow. It is the attraction between the particles that make it viscous.

Examples Think of 5 every day items that are viscous.
Can you find a way to change their viscosity? Temperature

Ideal Gas P1V1 = P2V2 T T2 The three laws we will look at take a variable out of this equation and hold it constant.

Ideal Gas Boyle’s Law P1V1 = P2V2
Temperature stays constant, so we remove it from the combined gas equation. This was the marshmallow experiment.

Ideal Gas Boyle’s Law – Pressure increases, volume decreases. They are inversely proportional.

Ideal Gas Charles’ Law V1 = V2 T1 T2 Pressure stays constant
Frozen balloon Room temp balloon

Ideal Gas Charles’ Law

Ideal Gas Gay-Lussac’s Law P1 = P2 T T2 Directly proportional

Ideal Gas

Practice Problems Charles’ Law
If I have 45L of helium in a balloon at 298K and increase the temperature of the balloon to 328K, what will the new volume of the balloon be?

Practice Problem Charles Law
I have 130L of gas in a piston at a temperature of 523K. If I cool the gas until the volume decreases to 85L, what will the temperature of the gas be?

Practice Problem Gay-Lussac’s Law
10.0 L of a gas is found to exert kPa at 298K. What would be the required temperature to change the pressure to kPa?